This invention relates in general to disposing of drill cuttings that are generated in the process of drilling oil and gas wells. This is accomplished by injection into the annulus around the well casing.
When drilling a subsea well, cuttings are generated. The cuttings are small pieces of earth formation formed by the drill bit. The cuttings are circulated along with drilling fluid up a riser to the drilling platform, where they are separated. The drilling fluid is circulated back into the well.
In the past, it was a common practice to dump the cuttings into the sea. Particularly with oil based drilling fluids, this practice is no longer acceptable. The cuttings would be contaminated with oil and result in pollution. One disposal technique is to inject the cuttings back into a well. The well could be the well that is being drilled or an adjacent well. The cuttings are ground and pumped in a slurry down an annulus between strings of casing and into a porous earth formation. Subsequently, the well receiving the injected cuttings is completed into a producing well.
Injection systems normally pump the cuttings slurry through a port in a wellhead housing at the upper end of the well. The wellhead housing contains at least one concentric tubular member, such as a casing hanger and a string of casing extending into the well. An annular clearance is located between the tubular member and the housing, the annular clearance communicating with the casing annulus. The stream of cuttings strikes the wall of the casing hanger or casing and flows down the annular clearance into the casing annulus.
The stream of cuttings is abrasive because of the cuttings. Consequently, the stream tends to erode the tubular member where it impinges.
The invention comprises a cuttings injection target or deflection plate. The deflection plate is mounted in proximity to the outlet of the injection port for contact by the stream as it discharges from the outlet for protecting the inner tubular member from contact by the stream. Preferably, the deflection plate is on an inner end of a protection sleeve that is mounted in the injection port extending through the wall of a wellhead housing. Exit holes in the sleeve upstream of the deflection plate allow injected cuttings discharge to the annulus. Drill cuttings impact upon the deflection plate and deflect to exit through the holes. This reduces the wear by erosion on the casing hanger by deflecting the impact and allowing the cuttings to escape through the holes. The deflection plate preferably has a wear resistant surface, such as a hardfacing.
The sleeve can be periodically removed and checked during cuttings injection operations. Where annulus space is limited, provisions can be made to enlarge the inner end of the passage through the wall of the wellhead housing and shorten the sleeve so that the sleeve outlet holes are inside the enlarged outlet end of the injection passage.